1. Field of the Invention
The present invention relates to a workpiece carrier and, more particularly, to a workpiece carrier for transport by at least one belt conveyor, especially a double belt conveyor.
2. Related Art
A workpiece conveyor for conveying one or more workpieces by means of a belt conveyor, especially a double belt conveyor, is described in European Patent Document EP 37 361 B1. This sort of workpiece carrier is used in industrial assembly and manufacturing plants. The workpiece carrier or support is placed on the belt conveyor and is conveyed by a frictional connection between the belt conveyor and the workpiece carrier. These workpiece carriers are brought to a stop in front of transfer points to other belt conveyors or processing stations. This usually happens by means of a stopping device having a traveling holding element that can travel into the motion path of the workpiece carrier and thereby stop it. If the workpiece carrier is stopped, the belt conveyor slides past the workpiece carrier under the workpiece carrier. If the workpiece carrier is no longer braked, i.e. the holding element of the stopping device releases the workpiece carrier so that it can travel over the motion path. The workpiece carrier still requires a predetermined time interval in order to reach the processing station or the transfer point by means of the belt conveyor. Still more time can be lost by the motion of the belt conveyor under the workpiece carrier during travel. In any case the total machine cycle time for the concerned fabrication and assembly unit increases.
It is an object of the present invention to provide an improved workpiece carrier for a belt conveyor of the above-described kind, which does not suffer from the above-mentioned disadvantages.
According to the invention the workpiece carrier for conveying one or more workpieces with at least one belt conveyor comprises at least one energy storage means, which stores energy transferred to it when the workpiece carrier is stopped on or braked against the at least one belt conveyor and which releases the stored energy when the workpiece carrier is no longer braked or stopped on the at least one belt conveyor, whereby the workpiece carrier experiences an additional acceleration.
The workpiece carrier according to the invention has the advantage that during travel, i.e. when the workpiece carrier is no longer braked, less time is lost.
In an especially simple and advantageous embodiment of the invention a spiral spring is put under tension or a coil spring is compressed by means of the conveyor motion of the belt conveyor via a coupling element, advantageously a friction wheel or contacting piece, when the workpiece carrier is braked against or stopped on the belt conveyor. In another preferred embodiment the friction properties of the workpiece carrier on the conveyor belt may be optimized by means of a layer or coating with anisotropic friction properties. The amount of friction between the coupling element and the belt conveyor may be improved by a pressing spring element acting on the coupling element. If the pressing spring is dimensioned so that the workpiece carrier contacts on the belt conveyor only via the energy storing means, all undesirable friction may be eliminated.
Further features and advantages are described in the detailed description and claims appended hereinbelow.